Stem Size Distribution Research Articles

Floristic and structural distinctness of monodominant Gilbertiodendron dewevrei forest in the western Congo Basin

Background and aims – The forests of the Congo Basin contain high levels of biodiversity, and are globally important for carbon storage. In order to design effective conservation strategies, and to accurately model carbon stocks, a fine-scale understanding of the different forest types that make up this forest block is needed. Monodominant Gilbertiodendron dewevrei forest covers large areas of the Congo Basin, but it is currently unclear whether it is sufficiently distinct from adjacent mixed terre firme forest to warrant separate treatment for conservation planning and carbon calculations. This study aimed to compare the structure and diversity of monodominant and mixed forest, and ask whether there is a unique vascular plant community associated with G. dewevrei forest. Material and methods – We utilised a combination of plot data and herbarium specimens collected in the Sangha Trinational (a network of protect areas in Cameroon, Central African Republic, and the Republic of Congo). Plot inventories were used to compare G. dewevrei forest and mixed forest for stem density, basal area, above ground biomass, stem size distribution, species diversity, and species composition. In addition, a database of 3,557 herbarium specimens was used to identify species of vascular plant that are associated with G. dewevrei forest. Key results – Gilbertiodendron dewevrei forest is distinct in both structure and species composition from mixed forest. Gilbertiodendron dewevrei forest has a lower stem number (of trees ≥ 10 cm), but a greater proportion of larger trees (> 70 cm), suggesting higher carbon stocks. The species composition is distinct from mixed forest, with 56 species of vascular plant significantly associated with G. dewevrei forest. Conclusion – Monodominant G. dewevrei forest in the Sangha Trinational is both compositionally and structurally distinct from mixed forest. We therefore recommend this forest type be considered separately from mixed forest for conservation planning and carbon stock calculations.

Influence of Landscape Characteristics on Wind Dispersal Efficiency of Calotropis procera

Rubber bush (Calotropis procera), a perennial invasive milkweed, infests large swathes of pastoral land in northern Australia and Queensland, diminishing pasture productivity. The seeds of rubber are small with fluffy pappi that confer buoyancy during wind dispersal. Long-distance seed dispersal (LDD) by wind is dependent in part on seed terminal velocity, the height of release above the ground, the surrounding vegetation, and wind parameters such as speed and vertical turbulence. Using empirical dispersal data, spatial population distribution, and historical knowledge of three experimental sites, we examine how seed traits can interact with environmental features to promote dispersal. We expected naturalised rubber bush populations to have the following: (1) higher spatial autocorrelation on open plains where dispersal distances are maximised compared to hilly habitats or those with tall vegetation; (2) southeast to northwest directional bias aligned to prevailing winds; and (3) patchy satellite populations ahead of an infilled continuous main front. Seed dispersal kernels were estimated by releasing seeds from dehiscent fruit for four periods of ten minutes each at three locations from a fixed height while monitoring wind speed. Five alternative models were fitted to the seed dispersal data, of which the log-logistic (Kolgomorov–Smirnov test p = 0.9998), 3-parameter Weibull model (K-S p = 0.9992), and Weibull model (K-S p = 0.9956) provided the best fit in that order. Stem size distribution was similar at the leading edges of populations at all sites (F10, 395 = 1.54; p = 0.12). The exponential semivariogram model of the level of spatial autocorrelation was the best fit and was adopted for all sites (Tennant Creek (TC), Helen Springs (HS) and Muckaty (MU) sites (R2 = 63.8%, 70.3%, and 93.7%, respectively). Spatial autocorrelation along the predicted southeast-to-northwest bearing was evident at all sites (TC kriging range = 236 m; HS = 738 m and MU = 1779.8 m). Seed dispersal distance was bimodal and dependent on prevailing wind conditions, with short distance dispersal (SDD) up to 55 m, while the furthest propagules were 1.8 km downwind in open environments. Dispersal directions and distances were pronounced on plains with short or no vegetation, compared to hilly locations or areas with tall vegetation. In designing management strategies, it should be noted that invasion risk is greater in frequently disturbed open landscapes, such as pastoral landscapes in Northern Australia. Infestations on open xeric grassland plains with shrubby vegetation should be a priority for rubber bush control to maintain high levels of productivity in beef production systems.

A smaller femoral stem is needed for asian females.

Current femoral implants are manufactured based on Western anatomical structures and may be too large for smaller physiques, such as those of Asian females. This study reviewed the femoral stem size distribution used in a high-volume total hip arthroplasty (THA) practice and evaluated malalignment in patients receiving a size one implant. A consecutive cohort of female patients self-reported as Asian (257 patients, 331 hips) or Caucasian (158 patients and 190 hips) were retrospectively evaluated. A single femoral stem type was used in all cases, performed by a single surgeon. Global hip offset (GHO) and leg length difference (LLD) were measured before and 6weeks following THA. Differences between races were evaluated through Mann-Whitney U tests and chi-squared tests for continuous and categorical variables, respectively. The proportion of size one implants was higher amongst Asian patients (20.5%) than Caucasian patients (2.6%) (p < 0.001). A LLD greater than 6mm was noted in 24.6% of size one patients and 11.4% of all other sizes (p = 0.010). Varus malalignment occurred in 47.9% of size one patients and 22.1% of all other sizes (p < 0.001). No fractures occurred in size one patients, and nine fractures (one intraoperative and eight post-operative) occurred in all other sizes (p = 0.258). The high proportion of size one stems required in Asian females and the higher incidence of LLD > 6mm and varus malalignment suggest a distinct need for smaller femoral implants, especially for Asian females.

Estimating Species-Specific Stem Size Distributions of Uneven-Aged Mixed Deciduous Forests Using ALS Data and Neural Networks

Sustainable forest management requires accurate fine-scale description of wood resources. Stem size distribution (SSD) by species is used by foresters worldwide as a representative overview of forest structure and species composition suitable for informing management decisions at shorter and longer terms. In mixed uneven-aged deciduous forests, tree data required for SSD estimation are most often collected in the field through traditional forest management inventories (FMIs), but these are time-consuming and costly with respect to the sampled area. Combining FMIs with remote sensing methods such as airborne laser scanning (ALS), which has high potential for predicting forest structure and composition, and is becoming increasingly accessible and affordable, could provide cheaper and faster SSD data across large areas. In this study, we developed a method for estimating species-specific SSDs by combining FMIs and dual-wavelength ALS data using neural networks (NNs). The proposed method was tested and validated using 178 FMI plots within 22,000 ha of a mixed uneven-aged deciduous forest in Belgium. The forest canopy was segmented, and metrics were derived from the ALS point cloud. A NN with a custom architecture was set up to simultaneously predict the three components required to compute species-specific SSDs (species, circumference, and number of stems) at segment level. Species-specific SSDs were thereafter estimated at stand level by aggregating the estimates for the segments. A robustness test was set up using fully independent plots to thoroughly assess the method precision at stand-level on a larger area. The global Reynolds index for the species-specific SSDs was 21.2 for the training dataset and 54.0 for the independent dataset. The proposed method does not require allometric models, prior knowledge of the structure, or the predefinition of variables; it is versatile and thus potentially adaptable to other forest types having different structures and compositions.

Prediction of forest parameters and carbon accounting under different fire regimes in Miombo woodlands, Niassa Special Reserve, Northern Mozambique

Miombo woodlands are the most extensive dry forest type in southern Africa, covering ca. 1.9 million km2 across seven countries. Fire is a key ecosystem process that has structured miombo for the last 200,000 years. However, how fires affect the ecosystem's functioning is not well understood. In this study, we used the individual-based forest model called FORMIND to analyze the carbon balance in the miombo woodlands of Niassa Special Reserve (NSR), northern Mozambique. The 42.000 km2 NSR represents the most important conservation area in Mozambique (~31% of the total conservation area in the country) and of miombo woodlands worldwide. Long-term inventory data from 2004 to 2019 for NSR were used to calibrate FORMIND. The primary ecosystem processes of this model are tree growth, mortality, regeneration, and competition. Fire is set as one of the main factors that affect these processes, after the woodland reaches an equilibrium at 200 years of age. We also calculated the Net Present Value (NPV) of carbon credits resulting from altering the fire regime (e.g., reducing or eliminating fires). The FORMIND model successfully reproduced important characteristics of the woodlands (aboveground biomass, stem size distribution and basal area). NPV estimates of above-ground woody biomass carbon stocks were highly dependent on the woodland age. The maximum NPV estimates were generated for a 30-year project starting with 200 year old woodlands (the current forest age) at 192–1339 USD based on a realistic range of carbon values (i.e., 3–20 USD MgCO2e−1). While fire plays an important role in miombo woodlands by reducing stock and changing species composition, its effects on the capacity of the woodland to mitigate the effects of climate change varies depending on the age of stands. Our results show that FORMIND model reliably reproduce the field inventory data, thus can be used to improve carbon accounting standards. We recommend the development of a fire management system to sustain the miombo woodlands of NSR for multiple reasons. NSR is a globally significant protected area, but perhaps more importantly it could become a regional example for how to improve miombo woodland management. Given that miombo woodlands provide a myriad of ecosystem services to rural Africans, investing in improving fire management could increase the benefits to local communities. Altering fire regimes could improve habitat quality and promote greater resilience to climate change while sequestering carbon. In addition, local employment opportunities in fire management could be created via carbon financing from a carbon project. However, much more outreach and education will be needed to local and national stakeholders for fire management to be perceived more positively and realize the potential to generate multiple benefits for nature and people.

Geographic distribution and the reproductive and demographic ecology of two congeneric seeder and resprouter tree species

The distribution limits of species are mainly related to climate but other environmental factors such as soil and fire may also play an important role in local population dynamics. Species that re-establish from seed after a severe disturbance (seeder species) should have different functional attributes from species that can survive a disturbance by vegetative regeneration (resprouters). The functional attributes will influence the establishment and survival of individuals and for trees, the stem size distributions provide a view of the history of the populations and may indicate the trajectories of the populations as they age. Two congeneric tree species – Allocasuarina fraseriana (a resprouter) and A. huegeliana (a seeder) are dominant to subdominant trees in forest and woodland vegetation of south western Australia and illustrate useful comparisons of functional attributes and population structures. Both species occupy fire prone vegetation, bear seeds in serotinous cones and are considered to regenerate new individuals after fire events. The seeder (Allocasuarina huegeliana) has smaller cones and seeds and more seeds cone-1 than the resprouter (A. fraseriana). The cones of the resprouter provide more protection against heat to the contained seeds than the seeder. It is generally considered that species in fire prone environments often rely on disturbance to provide suitable conditions for regeneration and recruitment between disturbances is poor. For a species killed by disturbance population structures years after the disturbance would be expected to be unimodal while a resprouter would have a multimodal structure, as adults would survive and remain in the population with the new recruits. Unexpectedly population structures for the two species we studied were very similar when compared at an overall landscape scale. We attribute this mainly to the ability of the species to recruit interfire. Best seedling recruitment does occur after fire, as this provides an environment with more nutrients and reduced competition for the seedlings. However interfire recruitment can be abundant in some habitats. The degree to which this occurs may vary in relation to co-occurring tree species and landscape position. In general, fuel reduction fires are being used to reduce the danger of high intensity fires as the climate becomes drier and hotter in parts of southern Australia and mild fires will influence recruitment of both species. Low intensity surface fires will remove interfire recruits of the seeder species, but may increase the density of small plants of the resprouter. Adults are unlikely to be damaged but size class structures will be different from those after stand replacing fires.

Structural development following stand-replacing disturbance in a boreal mixedwood forest

Knowledge of forest stand successional pathways, and responses to disturbances, is crucial for improved sustainable management of the resource. Forest structure, one attribute of which is the size and height distribution of trees in a stand (known as the stem size distribution; SSD), is highly sensitive to changes in stand dynamics. However, monitoring changes in SSD can be difficult and costly, especially across large spatial extents and by different disturbance types and species groups. As a result, forest managers increasingly utilise three-dimensional remote sensing such as airborne laser scanning (ALS) as a means of modeling forest structure in a cost-effective and spatially consistent manner. In this study, approximately 7000 ALS-derived SSDs representing a chronosequence of over 50 years of forest disturbance in Alberta, Canada were used to evaluate differences in structural development by species groups and disturbance types. Stands were clustered into three structural development phases based on ALS-derived SSDs. Results showed no difference in SSDs for early development phases, but significantly higher proportions of trees in medium-sized diameter classes (up to 25 cm diameter at breast height) in previously burned stands than in previously harvested stands. For each structural development phase, in both burned and harvested stands, there was no significant difference in modeled SSD among species groups. No difference in SSD for each phase was also seen when comparing previously burned to harvested stands for mixed species and white spruce stands. However, aspen and pine-dominated stands had significantly higher proportions of larger trees in burned stands than harvested stands in the second and third phase of structural development. Results from this study provide valuable insights to the current state of the forest, as well as an improved understanding of the general patterns of structural development following disturbance.

Enhancing the Estimation of Stem-Size Distributions for Unimodal and Bimodal Stands in a Boreal Mixedwood Forest with Airborne Laser Scanning Data

Stem size distribution (SSD), which describes tree frequencies in diameter classes within an area, has a variety of direct and indirect applications that are critical for forest management. In this study, we evaluated which structural characteristics derived from Airborne Laser Scanning (ALS) data were best able to differentiate between unimodal and bimodal stands in a managed boreal mixedwood forest in Alberta, Canada. We then used wall-to-wall ALS data to predict (for 20 m-by-20 m grid cells) the parameters of a Weibull SSD in unimodal cells, and a Finite Mixture Model (FMM) in bimodal cells. The resulting SSDs were evaluated for their fit to ground plot-measured SSDs using an Error Index (EI). We found that the variance of ALS return heights was the best metric for differentiating between unimodal and bimodal stands, with a classification accuracy of 77%. Parameters of both the Weibull and FMM distributions were accurately predicted (r2 ~ 0.5, Root Mean Square Error (RMSE) ~ 30%), and that differentiating for modality prior to estimating SSD improved the accuracy of estimates (EI of 49.13 with differentiation versus 51.31 without differentiation). Unique to our presented approach is the stratification by SSD modality prior to the modelling of distributions. To achieve this, we apply a threshold to an ALS metric that allows SSD modality to be distinguished for each cell at the landscape level, and this a priori information is then used to ensure that the appropriate distribution is modelled. Our approach is parsimonious and efficient, enabling improved accuracy in SSD estimation across diverse landscapes when ALS data is the sole data source.

The effects of number of stems per stool on cutting productivity in coppiced &lt;i&gt;Eucalyptus&lt;/i&gt; plantations

A time study was conducted to determine whether stem crowding had any impact on harvester productivity in stands. This represents an important element when trying to balance the advantages and disadvantages of coppice management in fast growing plantations designated for mechanized harvesting (i.e. machine felling, delimbing, debarking and cross-cutting). The study material consisted of 446 coppice stems, half of which grew as single stems per stool and half as double stems per stool as a result of different coppice reduction strategies. The dataset was balanced and randomized, with both subsets replicating exactly the same stem size distribution and the single and double stems alternating randomly. Harvester productivity ranged between 6Â and 50 m under bark per productive machine hour, following the variation of tree diameter from 10 to 40 cm at breast height (1.37 m according to South African standards). Regression analysis indicated that both tree size and stem crowding (e.g. one or two stems per stool) had a significant effect on harvester productivity, which increased with stem size and decreased with stem crowding. However, operator experience may overcome the effect of stem crowding, which was not significant when the harvester was manned by a highly experienced operator. In any case, the effect of stem size was much greater than that of stem crowding, which resulted in a cost difference of less than 10%. However, this figure excludes the possible effects of stem crowding on volume recovery and stem development, which should be addressed in the future.Eucalyptus grandis3

Simulating carbon stocks and fluxes of an African tropical montane forest with an individual-based forest model.

Tropical forests are carbon-dense and highly productive ecosystems. Consequently, they play an important role in the global carbon cycle. In the present study we used an individual-based forest model (FORMIND) to analyze the carbon balances of a tropical forest. The main processes of this model are tree growth, mortality, regeneration, and competition. Model parameters were calibrated using forest inventory data from a tropical forest at Mt. Kilimanjaro. The simulation results showed that the model successfully reproduces important characteristics of tropical forests (aboveground biomass, stem size distribution and leaf area index). The estimated aboveground biomass (385 t/ha) is comparable to biomass values in the Amazon and other tropical forests in Africa. The simulated forest reveals a gross primary production of 24 tcha-1yr-1. Modeling above- and belowground carbon stocks, we analyzed the carbon balance of the investigated tropical forest. The simulated carbon balance of this old-growth forest is zero on average. This study provides an example of how forest models can be used in combination with forest inventory data to investigate forest structure and local carbon balances.

A neutral vs. non-neutral parametrizations of a physiological forest gap model

Tropical forests are vital ecosystems which provide numerous ecological functions and forest models can be used to simulate their dynamics. However, due to the high species diversity of tropical forests and the common lack of detailed knowledge about these species, simulating the behavior of each species separately is not feasible. Therefore, species with common characteristics are usually aggregated into species groups.Although the number of species groups is likely to be an important characteristic of forest models, little research has been done on its effect on the results of the model. In this article, we compare the effect of the number of species groups using a physiological forest gap model and review our results using 28 years of field data from a 50ha forest plot in Panama as well as a chronosequence over four centuries from the same area. The number of simulated groups ranged from 1 to 4, 9 and 16. The parameterization with a single species group is a “neutral” parameterization with all simulated trees being ecophysiologically identical.The number of groups turned out to be an important characteristic of the model which influences its results on a fundamental level. Steady-states characteristics of forests like stem-numbers and stem-size distributions can be successfully simulated with even a single species group while modeling the long-term dynamics requires a higher number of groups. On the downside, a higher number of groups makes parameterization and fitting of the model more difficult. We conclude that the number of species groups is a vital characteristic of a forest model which has far-reaching consequences for its results and needs to be chosen with care.

Modelling the impact of shallow landslides on forest structure in tropical montane forests

Shallow landslides are an important type of natural ecosystem disturbance in tropical montane forests. Due to landslides, vegetation and often also the upper soil layer are removed, and space for primary succession under altered environmental conditions is created. Little is known about how these altered conditions affect important aspects of forest recovery such as the establishment of new tree biomass and species composition. To address these questions we utilize a process-based forest simulation model and develop potential forest regrowth scenarios. We investigate how changes in different trees species characteristics influence forest recovery on landslide sites. The applied regrowth scenarios are: undisturbed regrowth (all tree species characteristics remain like in the undisturbed forest), reduced tree growth (induced by nutrient limitation), reduced tree establishment (due to thicket-forming vegetation and dispersal limitation) and increased tree mortality (due to post-landslide erosion and increased susceptibility). We then apply these scenarios to an evergreen tropical montane forest in southern Ecuador where landslides constitute a major source of natural disturbance. Our most important findings are(a)On the local scale of a single landslide tree biomass recovers within the first 80 years after landslides for most scenarios, but it takes at least 200 years for the post-landslide forest to reach a structure (in terms of stem size distribution) similar to a mature forest. On this scale forest productivity is reduced for most regrowth scenarios. Changes in different tree species characteristics produce distinct spatio-temporal patterns of tree biomass distribution in the first decades of recovery within the landslide disturbed area. These patterns can potentially be used for identifying the dominant processes that drive forest recovery on landslide disturbed sites.(b)On the larger scale of the landscape overall tree biomass is reduced by 9–15% due to landslide disturbances. Overall forest productivity is only slightly reduced (<6%), but landslides increase landscape heterogeneity and produce hotspots of biomass loss and ‘blind spots’ of forest productivity. Thus landslides have a strong impact on the distribution of biomass in tropical montane forests.This study demonstrates that dynamic forest models are useful tools for complementing field based studies on landslides; they allow for testing alternative hypotheses on different sources of heterogeneity across spatial scales and investigating the influence of landslides on long-term forest dynamics.

A large-scale inventory of liana diversity in tropical forests of South Eastern Ghats, India

Among the plant life-forms, lianas, the wood climbers still remain less studied than trees. The forests of Eastern Ghats of India are also relatively under studied compared with the Western Ghats biodiversity hotspot. We conducted a large-scale, landscape-level investigation of liana diversity in six hill complexes of the South Eastern Ghats, which covers 4297 km2. We divided the study area into 6.25 km × 6.25 km grids and within each grid a 0.5 ha (5 m × 1000 m) transect was established and all lianas ≥1.5 cm diameter at breast height (dbh) were inventoried in 110 transects totalling a 55-ha area. Liana diversity totalled 143 species in 83 genera and 37 families in the 55 ha sampled. Of these 20 species (28.6%) were endemic to peninsular India and 7 (10%) species belonged to the rare and endangered category. Liana species richness ranged from 8–35 species and density 95–544 individuals per transect. A total of 32 033 liana individuals were enumerated in the 55 ha and the mean abundance was 291 individuals per transect. Across sites, liana abundance varied significantly, but not species richness and basal area. Asclepiadaceae (13 species, 9%) and Apocynaceae (11 species, 8%) constituted the most diverse liana families, followed by Papilionaceae, Vitaceae (10 each, 7%), Convolvulaceae, Mimosaceae, Oleaceae (8 each, 6%), Capparaceae, Rhamnaceae (7 each, 5%) and Menispermaceae (5 species, 3%). In liana stem size distribution, the lowest diameter class (1.5–3 cm dbh) accounted for greatest species richness (137 species, 96%), abundance (27 358 individuals, 85%) and basal area (13.5 m2, 36%). The stem twiners were the predominant climber type in terms of species richness (61 species, 42.65%), whereas the armed scramblers were abundant due to stem density (21 571 individuals, 67.34%). The dispersal modes of lianas, assessed by fruit types, revealed zoochory as the prevalent mode (85 species, 59%) indicating the faunal dependence of lianas in the Eastern Ghats landscape. Liana diversity of the Eastern Ghats was compared with inventories made across the tropics. With these baseline data generated on lianas, the importance of biodiversity conservation of the already fragmented South Eastern Ghats region is underlined and potential areas of further research on liana ecology are suggested.

Do current stem size distributions predict future population changes? An empirical test of intraspecific patterns in tropical trees at two spatial scales

It is critical to understand the responses of tropical tree species to ongoing anthropogenic disturbances. Given the longevity of large trees and the scarcity of appropriately long-term demographic data, standing size distributions are a potential tool for predicting species' responses to disturbances and resultant changes in population structure. Here we test the utility of several different measures of size distribution for predicting subsequent population changes at the intraspecific level using demographic records from two subsampled 50-ha tree plots in Malaysia (Pasoh and Lambir). Most measures of size distribution failed to successfully predict population change better than random; however, the ‘coefficient of skewness’ (a measure of the relative proportion of small vs. large stems in a population) was able to correctly predict the direction of population change for approximately three-quarters of species at both sites. At Pasoh, the magnitude of this relationship decreased with adult stature and rate of turnover, but was unrelated to sapling growth rates at either site. Finally, using data for species common at both forests, we found that size distributions were generally uninformative of subsequent differences in population change between sites (only median dbh correctly predicted the direction of change for more species than random). Based on these results we conclude that some measures of intraspecific differences in size distribution are potentially informative of population trends within forests but have limited utility across broader spatial scales.

Regeneration changes in tree species abundance, diversity and structure in logged and unlogged subtropical rainforest over a 36-year period

The long-term effects of logging treatments on rainforest regeneration are difficult to quantify due to compounding interactions with natural dynamics, site characteristics and tree species. The aim of this study was to examine regeneration differences over a 36-year period in stands subjected to various levels of disturbance ranging from natural, through an increasing intensity of individual tree removal to intensive logging. Multivariate and univariate analyses of trees ≥10 cm diameter at 1.3 m above the ground (dbh) showed that regeneration responses were generally correlated with disturbance gradient. In the undisturbed controls there were gradual changes that had no significant effects on tree species richness and diversity, stem density, or diameter distribution. Gradual changes were also observed during the early stages of regeneration following logging. However, in logged sites changes in tree species richness and diversity, stem density and diameter distribution became more rapid with time, and significant changes were observed. Similar regeneration events across site and disturbance levels resulted in three identifiable stages. In the first stage, lasting about 10 years, stem density of abundant shade tolerant trees decreased with no discernable changes in tree species richness. In the second stage, also lasting about 10 years, tree species richness and diversity, as well as stem density decreased to minima due to localised species turnover and net mortality. In the third stage, recruitment surpassed mortality and reversed the net loss of both species and stems, as tree species assemblages began to return to pre-disturbance levels. Sites subjected to individual tree selective logging returned to their pre-logging states in all aspects within 35 years of logging, but diameter distribution of trees ≥40 cm dbh showed low density compared to that observed in the controls. After 15–30 years, sites subjected to more intensive logging returned to their pre-logging levels of stem densities, species abundance and richness, but after 35–44 years of regeneration this sites had low species diversity and high densities of both the small sized stems and shade intolerant tree species. More intensively logged sites also had a low density of shade tolerant tree species compared to the controls. This suggests that the restoration of forest structure takes considerably longer than the restoration of tree species richness and abundance following logging in these forests. A high rate of stand basal area growth and a modest diameter distribution of lager trees ≥40 cm dbh were observed in moderate tree selection logging. This indicates high timber production potential at moderate tree selection rate in this type of forest. However, if the stem size distribution of larger trees is to be maintained, a logging cycle longer than 50 years is necessary.

Analysis of biomass accumulation and stem size distributions over long periods in managed stands of Pinus sylvestris in Finland using the 3-PG model

We tested the performance of a process-based model (PBM) in relation to long-term mensuration data from two sites in Finland where the stands were up to 90 years old and had been thinned at approximately 5-year intervals over the last 50 years. The PBM used was based on the 3-PG (Physiological Principles to Predict Growth) model developed by Landsberg and Waring (1997), with modifications in the biomass allocation routine, for which we used data and calculations by Vanninen (2003) to estimate the allocation coefficients and turnover rates. Site fertility was estimated in terms of known site-type characteristics. The model was evaluated in terms of stand development and its ability to simulate responses to thinning; stem numbers after thinning were specified at the dates when the thinning took place. Stand development in terms of basal area, volume and mean diameter at breast height, closely followed the measured characteristics of all stands. Foliage mass predictions were close to estimates obtained by an empirical method. The analysis shows that, under normal thinning regimes, a range of different thinning intensities can be adequately described using a simple multiplicative model relating the proportion of volume and foliage mass removed to the corresponding proportion of stem numbers. This model, together with stem allometry data, described the "growth" in mean diameter after thinning, which simply reflected the removal of the smaller trees. These results indicate that, with a single set of parameter values, 3-PG can provide good descriptions of the growth patterns of trees-in this case Pinus sylvestris L.-over long periods, including growth after repeated thinning. One of the outputs from the 3-PG model is mean stem diameter (B): we show that it is feasible to estimate stem size distributions, which changed considerably over the life of these stands, from B using the Weibull function. This shows that, given information about the Weibull parameters for particular species and cultural systems, it should be possible to use stem numbers and the B obtained from the 3-PG model to produce information about stem size distributions from simulated data.

American chestnut sprout survival with biological control of the chestnut-blight fungus population

The American chestnut trees in Connecticut were reduced to understory shrubs by an imported fungus that causes lethal cankers. Chestnut blight disease was first reported in the United States in 1904, and in Connecticut in 1907. Hypovirulence is a virus disease of the fungus that reduces its virulence enough to allow the defense systems of the trees to restrict the fungus to the outer bark. Blight cankers on chestnut sprouts in a 1.4 ha wood-lot in central Connecticut were treated with hypovirulent strains from 1982 through 1986. Stem diameters were measured periodically. Stem size distribution has stayed consistently higher than in a comparable forest area with no treatment.

Feasibility of estimating stem size distribution from measurement on the largest trees in even-aged pure stands

Reconstruction of the size distribution of trees in stands provides critical information for assessing the effects of environmental changes on forests and for forest management. For furthering a method of such reconstruction, feasibility of estimating size distribution in stem volume from measurement of the largest trees was examined for even-aged pure stands of Pinus banksiana Lamb.and Larix gmelinii (Rupr.) Rupr. We tested what percentage of the largest trees should be included in obtaining a frequency distribution in stem volume that is not statistically different from the observed size distribution patterns. The –3/2 power, beta-type, and adjusted beta-type distribution functions were applied. Comparison of the observed stem frequencies and those estimated from measurement of the largest trees in a stand suggested that (i) the –3/2 power distribution, beta-type distribution, or adjusted beta-type distribution may be used for reconstruction of stem size variation in pure stands, if the overall size variation could be approximated by one of these functions; (ii) we can be at least 95% sure that the tree size pattern be expressed successfully with the –3/2 power distribution with tree samples of only the largest 20% in the stand, or with the beta-type distribution with the largest 30% in the stand; and (iii) the reliability decreases somewhat for the adjusted beta-type distribution. The second observation implies that reconstruction of the temporal changes in stand structure may be reliable up to the time when the stand density was about five times that of the trees used for fitting the –3/2 power distribution curve. Reliability may be warranted up to the stand density of about three times as the number of trees used for fitting the beta-type distribution. Other considerations and limitations are also discussed.

Feasibility of estimating stem size distribution from measurement on the largest trees in even-aged pure stands

Feasibility of estimating stem size distribution from measurement on the largest trees in even-aged pure stands

A comparison of above-ground component weights and element amounts in four forest species at Kirkton Glen

Trees, selected to cover the basal area size classes, were sampled at Kirkton Glen, part of Strathyre Forest, to determine the weights and element contents of the above-ground components. The main species present in this catchment were Sitka spruce, Norway spruce, European larch and Scots pine, all about 50 years old. Plots were established within representative areas of each species in the catchment, the stem size distribution was determined and a number of trees were selected for intensive sampling. Measurements of ring area and height increment were assembled to study tree growth, and showed that at all sites Sitka spruce was the most productive species. Component weights and nutrient contents from this mature site were compared with results from younger forested stands from other areas which had been determined using similar sampling strategies. Compilation of nutrient budgets also allowed evaluation of the consequences on element budgets of the various harvesting techniques to be assessed at this site, which is due to the progressively clear-felled.